Polymer preparation

ABSTRACT

Abstract of Disclosure 
     A process for preparing a conjugated polymer, which comprises polymerizing in a reaction mixture (a) an aromatic monomer having at least two reactive boron derivative groups selected from a boronic acid group, a boronic ester group and a borane group, and an aromatic monomer having at least two reactive halide functional groups; or (b) an aromatic monomer having one reactive halide functional group and one reactive boron derivative group selected from a boronic acid group, a boronic ester group and a borane group, wherein the reaction mixture comprises a catalytic amount of a palladium catalyst, and an organic base in an amount sufficient to convert the reactive boron derivative groups into -B(OH) 3   -   anions.

Field of the Invention

[0001] The present invention relates to a process for preparing apolymer such as a conjugated polymer for use in an optical device suchas an electroluminescent device.

Cross Reference to Related Applications

[0002] This case claims priority to the following, each of which isincorporated by reference:This is a continuation of Application No.09/518,991, filed March 3, 2000,which is a continuation of U.S.Provisional Serial No. 60/160,953 filed October 22, 1999; and claimspriority from UK Patent Application No. 9905203.7 filed March 5, 1999;andUK Patent Application No. 9925653.9 filed October 29, 1999.

Background of Invention

[0003] Organic electroluminescent devices are known which employ anorganic material for light emission. For example, W090/13148 describessuch a device comprising a semiconductor layer comprising a polymer filmwhich comprises at least one conjugated polymer situated betweenelectrodes. The polymer film in this case comprises a poly(para-phenylene vinylene) (PPV) film which is capable of light emissionwhen electrons and holes are injected therein. Other polymer layerscapable of transporting holes or transporting electrons to the emissivelayes may be incorporated into such devices. The bandgap of PPV andother poly(arylene vinylene) polymers may be tuned to modulate thewavelength, quantum efficiency and/or refractive index thereof, asdescribed in EP

[0004] Preparation of poly(arylene vinylene)s for use in optical deviceshas been conveniently carried out by a precursor route where thermalelimination of leaving groups gives rise to a conjugated polymer, or byother routes such as a dehydrohalogenation reaction. However,poly(arylene vinylene)s are not the only class of polymers which aresuitable for use in optical devices. Other aryl-containing polymers maybe useful and one route generally useful in the production of conjugatedpolymers is the Suzuki reaction (Synthetic Communications 11(7), 513,1981) . This reaction involves the use of a palladium-based catalyst, anaqueous alkaline carbonate or bicarbonate inorganic base and a solventfor the reactants and possibly the polymer product. The monomerreactants are typically a diboronic acid or diboronate monomer and adibromo monomer.

[0005] US 5777070 is directed to attempts to improve the Suzuki reactionto form conjugated polymers from aromatic monomers. US 5777070 indicatesthat such reactions require as a solvent a nonsolvent such as toluene.However, such nonsolvents are acknowledged to slow down the rate ofreaction. In order to overcome this disadvantage, US 5777040 proposesthe use of a phasecatalyst such as tricaprylmethyl ammonium chloridesold under the registered trade mark Aliquat to increase the rate ofreaction. Accordingly, the reaction mixture contains an organic solventsuch as toluene, an aqueous solution of an inorganic base such as sodiumbicarbonate, a catalytic amount of a palladium complex and a catalyticamount of the phase transfer catalyst.

[0006] The inventors of the present invention have identified a numberof drawbacks with the process described in US 5777070. Firstly, thereaction is very slow; reaction times are typically of the order of 12hours in order to produce a polymer having a molecular weight of thedesired order. Discolouration of the polymer product and decompositionof the catalyst become concerns with such long reaction times. Secondly,the reproducibility of the reaction is somewhat poor. The monomer ratiois generally used in the case of copolymerization to control themolecular weight of the product polymer. However, the present inventorshave noticed that the peak molecular weight of polymers producedaccording to the method disclosed in US 5,777,070 vary considerably fromreaction to reaction even when the starting monomer ratios the same.Experiments conducted by the inventors of the present invention haveshown that the peak molecular weight of the product polymer can vary byas much as about 100,000 for the same starting monomer ratio. Thirdly,the inventors of the present invention have also noticed thatsignificant foaming is observed and that side products are producedwhich complex strongly to the walls of the reaction vessel, when a glassreaction vessel is used. These are difficult to remove, and the reactionthus requires the use of specialized reaction vessels. The aboveproblems also make this a very difficult and expensive process to scaleup.

[0007] The present invention aims to overcome at least some of thedrawbacks mentioned above.

Summary of Invention

[0008] According to a first aspect of the present invention, there isprovided a process for preparing a conjugated polymer, which comprisespolymerizing in a reaction mixture (a) an aromatic monomer having atleast two boron derivative functional groups selected from a boronicacid group, a boronic ester group and a borane group, and an aromaticmonomer having at least two reactive halide functional groups; or (b) anaromatic monomer having one reactive halide functional group and oneboron derivative functional group selected from a boronic acid group, aboronic ester group and a borane group, wherein the reaction mixturecomprises a catalytic amount of a catalyst suitable for catalysing thepolymerisation of the aromatic monomers, and an organic base in anamount sufficient to convert the boron derivative functional groups into₃- anionic groups, wherein X is independently selected from the groupconsisting of F and OH.

[0009] The polymerisation proceeds by the coupling of the monomers viaelimination of a reactive halide group and a boronanionic group (₃).

[0010] According to one embodiment of the invention, the conversion ofthe boronfunctional groups to the boronate anionic groups (₃-) by theorganic base to form a salt having an organic cation is carried outunder nonconditions prior to polymerisation.

[0011] The boronate anionic group has the formula -B(OH)_(n)F_(m)-,wherein n+m=3 and n and m are each 0, 1, 2 or 3. The boronate anionicgroup is preferably a -B(OH)₃- group. However, the reaction may alsoproceed, for example, via a -B(OH)₂F⁻ anionic group using, for example,a tetraalkylammonium fluoride as the organic base.

[0012] The term conjugated polymer refers to either a fully conjugatedpolymer i.e. a polymer which is conjugated along the full length of itschain, or a partially conjugated polymer i.e. a polymer which containsconjugated segments together with nonsegments.

[0013] The term aromatic monomer refers to any monomer which has therespective functional groups directly substituted on one or morearomatic rings. In the case of monomers having more than one aromaticring, the functional groups can be substituted on either the same ordifferent aromatic rings. Examples of suitable types of monomersinclude, but are not limited to, arylenes, heterocylic aromaticmonomers, and fused aromatic systems such as biphenylenes, naphthalenesand fluorenes. Each monomer preferably comprises an arylene, aheteroarylene, a triarylamine, or a bisarylene vinylene. Each aromaticgroup within the monomer may be substituted or unsubstituted.particularly preferred types of monomers include dialkylphenylenes,dialkoxy phenylenes, substituted and non-substituted thiophenes andbenzothiadiazoles, and dialkylfluorenes such as 9,9-di-m-octylfluorenes.One or more of the monomers could also be a pre-formed oligomeric orpolymeric chain comprising several smaller units with the necessaryfunctional groups provided at the desired positions on the chain.

[0014] It is also envisaged that under the appropriate reactionconditions, this invention could also be extended to the use of monomersin which some or all of the functional groups are not directlysubstituted on an aromatic ring, in particular to other kinds ofunsaturated monomers.

[0015] Monomers particularly useful in the present invention includethose which may be polymerised to form a semiconductive conjugatedpolymer such as a semiconductive conjugated polymer for use in anoptical device such as an electroluminescent device. Such polymers maybe used in an emissive layer or as a hole transport or electrontransport polymer. Luminescent polymers are particularly useful in suchdevices. The conjugated polymer may be fully or partially conjugated,perhaps containing conjugated segments and may be a homopolymer, acopolymer or an oligomer, and may be a linear or a branched chainpolymer such as a dendrimer.

[0016] As described above, the monomers must each have the appropriatefunctional groups for the Suzuki reaction. In one arrangement, a firstreactive dihalide monomer is polymerised with a second monomer havingtwo boron derivative functional groups. In this arrangement the firstand the second monomers may be the same or different. Where the monomersare the same, a homopolymer is produced. Where the monomers aredifferent, a copolymer is produced. In a second arrangement, a monomerhaving a boron derivative functional group and a reactive halidefunctional group is polymerised to form a homopolymer. It is alsopossible to form copolymers from this second arrangement simply bypolymerising together two or more different types of monomers eachcontaining both functionalities.

[0017] Preferably, the reactive halide functional group on the reactivedihalide monomer or the monomer having the reactive halide functionalgroup is Br or I although it is possible to use instead groups such aschlorine, triflate (CF₃SO₃-), tosylate and mesylate.

[0018] With respect to the boron-derivative functional groups, theboronic acid group is represented by -B(OH)₂; the boronic ester group ispreferably -B(OR¹) (OR²) or -B(OR⁵O) and the borane group is preferably-BR³R⁴, wherein R¹ is a substituted or non-substituted C₁-C₆ alkyl groupand R₂ is H or a substituted or non-substituted C₁-C₆ alkyl group; R³and R⁴ are each independently substituted or non-substituted C₁-C₆ alkylgroups, and R⁵ is a substituted or non-substituted divalent hydrocarbonradical resulting in a 5 or 6 membered ester ring. Examples of suitablegroups as R⁵ include substituted or nonC₂ or C₃ alkylene groups, orsubstituted or non-substituted ortho- or metaphenylene groups.

[0019] Suitable boronic ester groups include, for example, the productsof esterification of the corresponding boronic acid group withmonovalent C₁-C₆ alcohols, ethane diols such as pinacol, propane diolsor ortho aromatic diols such as 1,2

[0020] The term "organic base" includes sources of hydroxyl ions andLewis bases such as those which create a source of hydroxyl ions incombination with water. The organic base should be soluble in an organicsolvent and/or an aqueous solvent. It is preferable to deliver theorganic base in the form of an aqueous solution thereof, as this iseffective at hydrolysing boronic ester or borane groups to thecorresponding boronic acid groups and then converting the boronic acidgroups to boronate anionic groups.

[0021] A single organic base or a mixture of different organic bases maybe used.

[0022] Examples of organic bases include alkyl ammonium hydroxides,alkyl ammonium carbonates, alkyl ammonium biscarbonates, alkylammoniumborates, 1,5-diazabicyclo[4.3.0]non-5-ene(DBN),1,6-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane(DABCO), dimethylaminopyridine (DMAP), pyridine, trialkylamines andalkylammonium fluorides such as tetraalkylammonium fluorides.

[0023] The organic base used in the method of the present invention ispreferably a tetraalkyl ammonium hydroxide such as tetramethyl ammoniumhydroxide, tetraethyl ammonium hydroxide or tetra-n-propyl ammoniumhydroxide.

[0024] In another preferred embodiment of the present invention, atetraalkyl ammonium carbonate or a tetraalkyl ammonium bicarbonate isused as the organic base. Other preferred bases are tetraalkylammoniumborates, particularly, tetraethyl ammonium borate. These bases areparticularly useful for reducing monomer degradation.

[0025] The most suitable organic base for any given system will dependon the nature of the monomers and solvent system employed. For example,in the case of the preparation of polyfluorenes from the boronic esterusing toluene as a solvent, a base selected from the group oftetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide ortetraisopropyl ammonium hydroxide is particularly preferred, withtetraethyl ammonium hydroxide being the most preferred of these organicbases.

[0026] The quantity of the base will depend on various factors such asthe type of particular base used and the type of boron derivativefunctional group used. However, it has to be present in a sufficientquantity to convert the boron derivative functional group into thecorresponding -B(X)₃ ⁻ anionic group, which is the reactive specieswhich is eliminated with the reactive halide functional group to effectpolymerisation. In the case that the boron-derivative group is a boronicester or a borane, the organic base should preferably be used in theform of an aqueous solution to provide sufficient water to hydrolyze theboronic ester or borane groups to the corresponding boronic acid groupsand convert the boronic acid groups into boronate anionic groups.

[0027] The use of one equivalent of organic base per boron-derivativefunctional group has been found to give fair degrees of polymerisationover a relatively long period of time. Preferably, at least 1.5 molarequivalents, further preferably at least 2 molar equivalents, of theorganic base per boron-derivative functional group are used. Forexample, molecular weights over 200,000 have been obtained in arelatively short period of time using 2.26 mole equivalents of organicbase per boron-derivative functional group.

[0028] The number of equivalents is defined by the functionality of thebase multiplied by the molar ratio of base to boron-derivativefunctional groups.

[0029] It is preferable that the reaction mixture includes a solvent inwhich the conjugated polymer is soluble. For example, in the case ofpolyfluorenes, non-polar aromatic solvents such as anisole, benzene,ethylbenzene, mesitylene, xylene, and particularly toluene arepreferred. It is also preferable that the reaction mixture includes asolvent in which the organic cation boronate salt produced by thereaction of the organic base with the boron-derivative functionalgroups, is soluble.

[0030] In the case that the boron-derivative functional group is aboronic ester or borane group, the reaction mixture should includesufficient water to hydrolyze the boronic ester or borane group to thecorresponding boronic acid group. The organic base, such as atetralkylammonium hydroxide or tetraalkyl ammonium carbonate orbicarbonate is preferably added to the reaction mixture in the form ofan aqueous solution to thereby providesufficient water to hydrolyze theboronic ester or borane groups to the corresponding boronic acid groups.According to one possible variation, it is envisaged that the alkylammonium hydroxide may alternatively be added in the form of a hydratedsalt thereof such as the trihydrate.

[0031] It is preferable to carry out the polymerisation in a singleliquid phase by using an organic solvent or solvent mixture in which allthe reaction components, i.e. the boronate salt produced by the reactionof the organic base with the boron-derivative functional groups and thedihalide monomers where applicable, are soluble, and with which waterpresent for hydrolysis of boronic ester groups or borane groups ismiscible.

[0032] In one embodiment, the reaction mixture further comprises anaqueous solution of an inorganic base, preferably an inorganic basewhich does not include alkali metal ions, such as NH₄OH. This ispreferred from the point of view of producing polymers of particularlyhigh molecular weight.

[0033] The catalyst used in the method of the present invention ispreferably a palladium catalyst. The palladium catalyst may be a Pd (0)complex or a Pd(II) salt. The Pd(0) complex is preferred, a Pd (Ph₃P)₄catalyst being particularly preferred. Typically, the amount ofpalladium catalyst in the reaction mixture is 0.01 to 1 mol %,preferably about 0.15 mol.%, based on the total number of moles ofmonomers used.

[0034] The inventors of the present invention have unexpectedly foundthat by conducting the reaction using an organic base rather aninorganic base as in US 5,777,070, the polymerization can be carried outwith faster reaction times and with better reproducibility. They havealso found that the use of an organic base eliminates the problem offoaming and the problem of side-products becoming strongly complexed tothe walls of the reaction vessel, whereby the need to utilizespecialized reaction vessels is eliminated. In addition, the fact thatalkali carbonates or alkali bicarbonates are not required for thereaction also has the additional advantage that it eliminates the needfor a final purification step to remove alkali metal contaminants, whichwould otherwise be required to avoid such contaminants detrimentallyaffecting the performance of the polymer material in many applications.Furthermore, the present inventors have found surprisingly that polymersprepared by this route have lower residual levels of palladium comparedto polymers prepared by prior art processes. This is particularlyimportant in the case that the polymer is to be used in a light-emittingdevice, since the presence of palladium is believed to have adetrimental effect on the optical performance of the device.

[0035] Furthermore, in the process of the present invention, themolecular weights grow gradually with time in these very controlledpolymerisations. This has the advantage that repeatable (consistent) anddesired molecular weights can be achieved by stopping the reaction atthe appropriate stage.

[0036] In a fourth aspect, the present invention provides a process forthe production of an optical device or a component for an opticaldevice. The process comprises providing a substrate and producing apolymer in accordance with the process as described above, whereby thepolymer is supported by the substrate. The polymer may be supported bythe substrate directly, for example where a polymer film is deposited orformed on the substrate, typically a transparent substrate.Alternatively, the polymer may be supported by the substrate indirectlywhere one or more intervening layers between the substrate and thepolymer are provided. The optical device may comprise a luminescentdevice such as an electroluminescent device in which the polymer isdisposed between a cathode and an anode. Where the polymer is anemissive layer, a hole transport layer may be provided between the anodeand the substrate and an electron transport layer may be providedbetween the polymer and the cathode.

Brief Description of Drawings

[0037] The present invention will now be described in further detail, byway of example only, with reference to the accompanying drawings, inwhich

[0038]FIGURE 1 shows a reaction scheme in accordance with the invention;

[0039]FIGURE 2 shows a schematic representation of an optical deviceaccording to the invention;

[0040]FIGURE 3 shows another reaction scheme in accordance with thepresent invention; and

[0041]FIGURE 4 shows examples of the boronate anions by which thepolymerisation proceeds.

Detailed Description

[0042]Figure 1 illustrates one possible route for providing poly2,7(9,9-di-n-octylfluorene) (F8a chain of di-n-octyl fluorene repeatingunits. A 2,7(9,9-di-n-octyIfluorene) diboronate (I) is reacted with acorresponding 2,7-dibromo-(9,9-di-n-octylfluorene) (II) in toluene inthe presence of a palladium catalyst such as Pd(PPh₃)₄ and an organicbase such as a tetraalkyl ammonium hydroxide, tetraalkyl ammoniumcarbonate or tetraalkyl ammonium bicarbcnate to produce polymer F8.

[0043] In an alternative embodiment of the present invention, thispolymer can be produced by, for example, the homopolymerization of2-bromo-(9,9-di-n-octylfluorene)-7-ethylenylboronate in toluene in thepresence of a palladium catalyst and an organic base.

[0044] Example 1Polymer F8 was produced according to the followingmethod. A three-necked 500ml round bottomed flask fitted with a glassstirring rod attached to an electrical mechanical stirrer, a Teflonstirring blade, and a reflux condensor (connected to a nitrogen line)was charged with 9,9-dioctylfluorene-2,7-di(ethylenylboronate) (4.773g,9.0mmol), 2, 7-dibromo-9, 9"-dioctylfluorene (4.936g, 0.027mmol),tetrakis-(triphenylphosphine)palladium (31.2mg, 0.027mmol) and toluene(90ml). The solution was stirred under nitrogen at room temperature forapproximately ten minutes. An aqueous solution of tetraethyl ammoniumhydroxide (30ml, 20% wt/vol.) was added to the stirring mixture at roomtemperature.

[0045] The stirring mixture was heated to and maintained at reflux(115°C oil bath temperature) for approximately two hours. Bromobenzene(1-2ml) was added to the mixture, which was allowed to stir at refluxfor a further hour before adding phenyl boronic acid (1.5-2.0g), afterwhich the mixture was allowed to stir at reflux for one hour.

[0046] The mixture was allowed to cool to room temperature and pouredslowly into 4 litres of methanol to precipitate the polymer. Thepolymer/methanol mixture was then filtered. The polymer isolated byfiltration was then further reprecipitated into methanol from toluenesolution.

[0047] The polymer obtained by this method had a peak molecular weightof 204,000. This and other molecular weights given below were measuredusing the Polymer Labs GPC system incorporating an LC1120 isocratic pumpand ERC-7515A Refractive Index Detector. The solvent used was THF at aflow rate of 1mI/min, and the temperature was controlled at 35°C. Thecolumn type was PL mixed (*2, 30cm) calibrated using PL 600polystyrenestandards.

[0048] Example 2

[0049] Polymer F8 was produced in exactly the same way as in Example 1except that the aqueous solution of tetraethyl ammonium hydroxide wasadded dropwise. The polymer obtained had a peak molecular weight: of229,000.

[0050] Example 3

[0051] Polymer F8 was produced in exactly the same way as in Example 1except that the reaction was carried out at half-scale in a 250ml flask.The polymer obtained had a peak molecular weight of 222,000.

[0052] Example 4

[0053] Polymer F8 was produced in exactly the same way as in Example 1except that an aqueous solution of ammonium hydroxide (10.45ml ammoniumhydroxide made up to 20ml with water) was further added to the monomerand toluene mixture prior to stirring under nitrogen at room temperaturefor ten minutes. No reaction was observed until the aqueous solution oftetraethyl ammonium hydroxide was added. The polymer obtained had a peakmolecular weight of 373,650.

[0054] Example 5

[0055] Polymer F8 was produced in exactly the sane manner as in Example1 except that an aqueous solution of an identical molar quantity oftetramethyl ammonium hydroxide was used instead of the aqueous solutionof tetraethyl ammonium hvdroxide. The polymer obtained had a peakmolecular weight of 150,500.

[0056] Example 6

[0057] Polymer F8 was produced in exactly to same way as in Example 1except that an aqueous solution of an identical molar quantity oftetrapropyl ammonium hydroxide was used instead of the aqueous solutionof tetraethyl ammonium hydroxide. The polymer obtained had a peakmolecular weight of 142,000.

[0058] Example 7

[0059] The reaction scheme for the synthesis of F8BT polymer usingBis(tetraethylammonium)carbonate as base is shown in Figure 3.

[0060] A 500ml reaction vessel was charged with9,9-dioctylfluorene-2,7-diethylenyl (4.773g,9.02-7-dibromobenzothiadiazole (2.6449g 9.0 mmol,tetrakistriphenylphosphine palladium 31.2 mg, and toluene 100 ml. Themixture was stirred at room temperature for 10 minutes under nitrogen.Bis(tetraethylammonium)carbonate (13.0g) dissolved in 20 ml ofde-ionised water was then added to the mixture, which was then allowedto stir at room temperature under flow of nitrogen for 20 minutes.

[0061] The reaction mixture was heated to and maintained at reflux undernitrogen for up to 18 hours (typically left overnight). During this timethe reaction mixture was stirred (setting rate 2-3) under an atmosphereof nitrogen.

[0062] Bromobenzene (1 ml) was then added and the reaction mixtureallowed to stir at reflux for 2 hours, after which phenyl boronic acidwas added (2 g) and the reaction mixture was allowed to stir at refluxfor a further 2 hours.

[0063] The mixture was allowed to cool to room, temperature and pouredinto 4l of methanol to precipitate the polymer. The polymer/methanolmixture was then filtered and the polymer was allowed to air dry on theBuchner funnel for five minutes. Aluminium foil was used to cover thetop of the Buchner funnel to minimise light exposure.

[0064] After purification, the final yield was ~ 3.05 g, 64%. The peakmolecular weight was found to be 175,000 (Mp) as determined by GPC.

[0065] Example 8

[0066] A further synthesis described particular case was carried out inaccordance with the in Example 7 except that, in this particular case amixed solvent system was used. The molecular weight obtained was (~50:50). The molecular weight obtained was ~ 350, 000 (Mp).

[0067] Example 9

[0068] 9,9-di-n-octylfluorene-2,7-ditethyleneboronate), 2,7-dibromo-9,9-dibromo-9,9-di-n-octylfluorene and a palladium catalystsuch as tetrakis(triphenylphosphine)palladium are dissolved intetrahydrofuran (THF). To this is added two equivalents of atetraalkylammonium hydroxide as an aqueous solution of concentration atleast 20% by weight. The mixture is stirred at room temperature under aflow of nitrogen for 20 min. During this time, the tetralkylammoniumdisalt shown as (1) in Figure 3 is formed and dissolves in the THF withthe other components to give a clear single liquid phase. The reactionis heated to the reflux temperature of THF (66°C) during which time thesolution viscosity increases as polymer molecular weight increases. Thereaction is usually complete within two hours.

[0069] As demonstrated above, particularly good results have beenachieved in this polymerisation by using a polar organic solvent inwhich the boronate salt and the dihalide monomers are soluble and whichis miscible with water (tetrahydrofuran) to provide a single phasereaction mixture. The polymerisation can be carried out at a relativelylow temperature and in a relatively short period of time. Furthermore,relatively high molecular weights can be achieved. The use of lowerreaction temperatures and shorter reaction times has the. addedadvantage that there is little if any palladium catalyst decomposition.

[0070] Example 10

[0071] 9,9-di-n-octylfluorene-2,7-di(ethyleneboronate),2,7-dibromo-9,9-di-n-octylfluorene and a palladium catalyst such astetrakis(triphenylphosphine)palladium are dissolved in a mixture oftoluene and THF (e.g. 1:1 mixture). To this is added two equivalents ofa tetraalkylammonium hydroxide as an aqueous solution of concentrationat least 20% by weight. The mixture is stirred at room temperature undera flow of nitrogen for 20 min. During this time, a tetraalkyl ammoniumdisalt of the kind shown as (1) in Figure 4 is formed as a white solidprecipitate suspended in a single liquid phase. The reaction is heatedto the reflux temperature of THF (66°C) during which time the solutionviscosity increases as polymer molecular weight increases. The reactionis usually complete within two hours.

[0072] As demonstrated above, this polymerisation can also be carriedout in mixtures of water-miscible organic solvents such as THF and nonwater-miscible non-polar solvents such as toluene. Although the disalttends to precipitate upon its in-situ formation to give a two phasesystem, the use of such a solvent mixture can be advantageous as somepolymers are more compatible with a polar solvent such as THF whereasothers are more soluble in non-polar solvents like toluene. The abilityto use such solvent mixtures means that far more polymer types can beprepared without a risk of premature polymer precipitation duringpolymerisation.

[0073] Example 11

[0074] 9,9-di-n-octylfluorene-2,7-di(ethyleneboronate),2,7-dibromo-9,9-di-n-octylfluorene and a palladium catalyst such astetrakis(triphenylphosphine)palladium are dissolved in tetrahydrofuran(THF). To this is added two equivalents of a tetraalkylammoniumhydroxide as an aqueous solution of concentration at least 20% byweight. The mixture is stirred at room temperature under a flow ofnitrogen for 20 min. During this time, a tetraalkyl ammonium disalt ofthe kind shown as (1) in Figure 4 is formed and dissolves in the THFwith the other components to give a clear single liquid phase. All thecomponents required for the polymerisation are present in the singleliquid phase. The reaction is heated to the reflux temperature of THF(66°C) during which time the solution viscosity increases as polymermolecular weight increases. After a certain amount of time (e.g. 1 hour)a proportion of a second organic solvent (e.g. toluene) is added and thereaction is continued at the same temperature until further molecularweight increase is not observed (usually a total reaction time of twohours).

[0075] As demonstrated in this example, good results have also beenachieved for this polymerisation by starting with a water-miscible polarorganic solvent (THF) as in Example 9, and adding a second miscibleorganic solvent in which the polymer is soluble as the polymerisationproceeds.

[0076] The molecular weights grow gradually with time in these verycontrolled polymerisations. This has the advantage that repeatable(consistent) and desired molecular weights can be achieved by stoppingthe reaction at the appropriate stage.

[0077] Comparative Example 1

[0078] A three necked 250 ml round bottomed flask fitted with a glassstirring rod attached to an electrical mechanical stirrer (Heidolph RZH2020), teflon stirring blade, reflux condenser (connected to a nitrogenline) was charged with 9,9-dioctylfluorene-2,7-di(ethylenylboronate)(4.8779g, 9.09 mmol, 98.8 % purity by HPLC),2,7-dibromo-9,9'-dioctylfluorene ((4.9360g, 9.0100% purity by HPLC)) andtoluene (90 ml). The solution was stirred under nitrogen for a 10minutes and then 3.5g of a surfactant solution (10g of Aliquat 336 andToluene 25g) (2.5mmol Alicuat 336) was added along with 20 ml of 2Msolution of sodium carbonate. The mixture was then stirred at roomtemperature under nitrogen for a further 15 minutes. The catalyst,tetrakistriphenylphosphinepalladium 31.2 mg, was then added and thereaction mixture was heated and maintained at reflux for is hours.

[0079] During this time the reaction mixture was stirred (setting rate2-3) under an atmosphere of nitrogen. The reaction mixture was observedafter 2 hours, but there was no sign of any production of the polymerindicating the slowness of the reaction.

[0080] After 20 hours brornobenzene (1 ml) was added and the reactionmixture was allowed to stir at reflux for a further 20 hours.

[0081] The mixture was allowed to cool to room temperature and pouredinto 4L of methanol to precipitate the polymer. The polymer/methanolmixture was then filtered and the polymer was allowed to air dry on theBuchner funnel for five minutes. Aluminium foil was used to cover thetop of the Buchner funnel to minimise light exposure.

[0082] Polymer F8 was produced twice according to the above. Thepolymers obtained had a molecular weight of 170000 and 230000,respectively, showing relatively poor reproducibility.

[0083]Figure 2 shows in a purely schematic way the order of layers in anelectroluminescent device generally designated 1. Disposed on substrate2, which is typically a transparent substrate such as glass, is anode 3which may be a layer of transparent indium tin oxide. Adjacent layer 2is hole transporting layer 3, which may be a polyethylenedioxythiophene, on which is disposed emissive layer 4, which may be apolymer according to the present invention. Layer 5 is an organicelectron transport layer. Layer 6 is a cathode which may be a lithiumaluminium layer.

[0084]

Claims
 1. 21. A process for coupling aromatic monomers, which comprisescoupling in a reaction mixture an aromatic monomer having at least oneboron-derivative functional group selected from the group consisting ofa boronic acid group, a boronic ester group and a borane group, and anaromatic monomer having at least one reactive halide functional group;wherein the reaction mixture comprises a catalytic amount of a catalystsuitable for catalysing the coupling of the aromatic monomers, and anorganic base including a tetraalkylammonium entity in an amountsufficient to convert the at least one boron-derivative functional groupinto -BX₃ ⁻ anionic group(s), wherein X is independently selected fromthe group consisting of F and OH.
 2. 22.A process for coupling aromaticmonomers, which comprises preparing under non-coupling conditions anorganic cation salt of an aromatic boronate monomer by the reaction ofan aromatic monomer having at least one boron-derivative functionalgroup with an organic base including a tetraalkylammonium entity in anamount sufficient to convert the at least one boron-derivativefunctional group into boronate anionic group(s) (-B(X)₃ ⁻) wherein X isindependently selected from the group consisting of F and OH, and thencoupling the organic cation salt of the aromatic boronate monomer withan aromatic monomer having at least one reactive halide functional groupin the presence of a catalyst suitable for catalysing the coupling byelimination of a halide functional group and a boronate anionic group.3. 23.A process according to claim 21 or 22, wherein X is OH.
 4. 24.Aprocess according to claim 21, wherein at least 1.5 equivalents of saidorganic base per boron-derivative functional group is provided in thereaction mixture.
 5. 25.A process according to claim 21, wherein atleast two equivalents of said organic base per boronfunctional group isprovided in the reaction mixture.
 6. 26.A process according to claim 21or 22, wherein the organic base is selected from the group consisting oftetraalkylammonium carbonates, tetraalkylammonium bicarbonates andalkylammonium hydroxides.
 7. 27.A process according to claim 21 or 22,wherein the organic base comprises R'R"' R"" NOH, wherein R' is a C₁ C₆alkyl group, and R", R"' and R"" are each independently hydrogen atomsor C₁ C₆ alkyl groups.
 8. 28.A process according to claim 27, whereinthe organic base is selected from the group consisting of (CH₃) ₄NOH,(C₂H₅) ₄NOH and (C₃H₇) ₄NOH.
 9. 29.A process according to claim 21 or22, wherein the organic base is a tetraalkylammonium carbonate or atetraalkylammonium bicarbonate.
 10. 30.A process according to claim 21or 22, wherein the organic base is used in combination with an aqueoussolution of an inorganic base.
 11. 31.A process according to claim 30,wherein the inorganic base is NH₄OH.
 12. 32.A process according to claim21 or 22, wherein the reaction is carried out in the absence of alkalimetal cations.
 13. 33.A process according to claim 21 or 22, wherein atleast one of the aromatic monomers is a 2,7(9,9-di-n-octylfluorene). 14.34.A process according to claim 21 or 22, wherein a solvent which ismiscible with water and in which the reactive components are soluble isused.
 15. 35.A process according to claim 21 for 22, wherein thecatalyst is a palladium catalyst.
 16. 36.A process according to claim22, wherein at least 1.5 equivalents of said organic base are reactedwith the aromatic monomer having at least one boron-derivativefunctional group to produce the organic cation salt.
 17. 37.A processaccording to claim 22, wherein at least 2 equivalents of said organicbase are reacted with the aromatic monomer having at least oneboron-derivative functional group to produce the organic cation salt.